Flooring and insulation question for the contractor types

Note on ridge vents:

Don't combine ridge vents with gable vents. They don’t play well together. 

JLC article on ridge vents with gable vents

Batts in crawl spaces always seem to end up retaining moisture and fostering mold growth and/or mildewy smells. The paper backing just adds organic matter that can decompose.

The vapor barrier on the dirt in the crawl is not there to increase the insulation or comfort level of the home, it's there to theoretically prevent soil gases from rising into the home, and make it slightly nicer to be in the crawl. Unless it's a perfect barrier that's taped to the exterior walls and has no holes, tears, seams, etc it's really not doing much.

Crawlspace encapsulation is a booming business in large parts of the country for these reasons and might be a good fit here, but it's expensive and may not even be possible with your limited clearance.

Spraying the subfloor with a couple of inches of closed cell Foam would be an actual, seamless vapor barrier that would completely air seal your floor while simultaneously giving you something like R18 insulation value. And it would add some strength to the structure, and would probably deaden some of the sound while walking on your floors. It's not as ideal as full encapsulation, but it would give you air sealing, an actual vapor barrier, a bunch of R value, and some other minor benefits. It's relatively expensive compared to other insulation options, but for a job as small as yours the total outlay might not be unbearable and you get some benefits that other insulation can't give.

SVreX said:

Note on ridge vents:

Don't combine ridge vents with gable vents. They don’t play well together. 

JLC article on ridge vents with gable vents

<looks at recently purchased house>

Oops.

Quietwalk under any floating floor would give you a nice warm and quiet feel under foot. We used it in some areas of our basement and it worked out great. 3mm thick so you don't lose appreciable ceiling height. 

SVreX said:

Note on the ceiling height... my suggestion of 3/4” insulation plus 5/8” of plywood is about equivalent to what you have in carpet and padding. 

You haven't seen my carpet and padding.  With the padding and pile, it's 3/8" at best.  The padding is maybe 1/8" and the carpet is less than 1/4".  Until it compresses under my feet, I can feel the seams in the T&G.

The entry door is 76" and barely clears the linoleum immediately in front of the entry.  I can cut the door, but the way they constructed the door frame it would require serious re-engineering.

Sorry to reiterate, but I absolutely will not entertain any idea of losing vertical space more than maybe 1/16".  Doing more than that will not only cause me to duck more through my doorways, but it will require pretty serious custom fitments to exterior doors to make them weather tight and still open over the flooring.  As it is right now, I have to duck to take off a T-shirt.  Adding 1-1/4" worth of insulation and underlayment is just not realistic.  I honestly won't even consider 3/8" hardwood.  I would consider 3/16" vinyl plank or laminate, but the thought of adding height to my floor gives me hives.

I think you'll have to bite the bullet and do spray-foam insulation, then. It'll be expensive, but it will stop the air infiltration and insulate the floor. The only problem I can see is that you've effectively made the adhesive layer between the house and the foam the vapor barrier, so your spray-foam installer will have to recommend a solution for that - it has to be a problem that's been solved because otherwise spray-foam would never work anywhere. 

In reply to chaparral :

Spray foam is it’s own vapor barrier. It doesn’t need an additional VB. 

I’m still not convinced they can run the equipment in a 12” crawl space. 

Spray foam installation- the gun plus hoses are nearly 18”